1. Field of the Invention
The present invention relates generally to magnetic recording/playback apparatus and more particularly to an improved flexible disc drive including a hinged hub assembly for clamping and driving a flexible disc.
2. Description of the Prior Art
The flexible disc recording medium, sometimes called a floppy disc or discette cartridge, is a Mylar disc enclosed in a plastic envelope having apertures for enabling the disc to be driven. Magnetic material is secured to the faces of the disc so as to provide the recording surfaces. The cartridge drive unit for receiving and making functional use of the cartridge typically consists of a drive mechanism, a read/write head, and means for receiving and loading the cartridge onto the drive mechanism and the read/write head.
In one type of prior art disc clamping apparatus, a door is opened, the cartridge is inserted into a slot between a drive spindle and a clamping structure, and the clamping structure then clamps the cartridge against the drive spindle. However, insertion of the disc does not provide positive cartridge registration and the disc may be damaged if the door is closed with the cartridge slightly misregistered.
In another prior art device a cartridge guide is utilized to direct the cartridge during insertion toward the spindle. In such devices the door is typically fixed to the cartridge guide by means of cams or linkages so that when the door is closed the cartridge is moved into registration with the drive spindle. However, these devices rarely provide for accurate disc-spindle alignment. Because of the misalignment associated with some prior art devices, registration is obtained only as long as the door is slowly closed such that the disc is gradually moved along the spindle and into registration therewith. However, it has been found that when the door is slammed, typically the disc becomes deformed. Consequently, since the cartridges are somewhat fragile and subject to wear and damage from mistreatment, the useful life of a cartridge is less than it could be if accurate alignment was provided.
In addition, it should be noted that when the disc is loaded, the spindle is normally rotating at its prescribed angular velocity, whereas the disc clamping mechanism is normally stationary and must be driven by the spindle. Accordingly, the disc clamping mechanism must be accelerated in order to reach the angular velocity of the spindle. Furthermore, a certain resistance to rotation is associated with the flexible disc due to its inertia and frictional engagement with the walls of the plastic envelope. Consequently, upon starting, the angular velocity of the disc is different from that of the disc clamping mechanism, and the angular velocity of the spindle is different from that of the disc. Because of these differences in angular velocities, the clamp tends to scuff and sometimes to destroy the magnetic surfaces of the flexible disc in the clamping area.
Still another prior art device employed a rotatable annular hub clamp and a collet having a plurality of spaced apart, flexible pivotable clamping fingers which cam the disc along the spindle into registration with a disc registration surface. A lip of the hub clamp continuously urges the clamping fingers to squeeze radially inwardly against a spindle registration surface. In addition, a ring having disc aligning fingers is sandwiched between the hub clamp and the collet and serves to initially engage the inner periphery of the disc so as to enable the clamping fingers to cam the disc. Because of the pivotal and the temperature requirements, the resilient clamping fingers are subject to fatigue and to decreased clamping effectiveness after extended usage in high temperature environments. Also, since the clamping fingers are widely spaced apart, they are inefficient in transferring driving torque from the rotating spindle to the hub assembly.
Examples of the prior art devices are found in U.S. Pat. No. 3,898,814 issued Aug. 12, 1975, to Albert S. Chou, Yang Hu Tong, Harold C. Medley and Warren L. Dalziel entitled "Mechanism For Clamping And Driving A Flexible Disc"; U.S. Pat. No. 3,678,481 issued July 18, 1972, in the name of Warren L. Dalziel, Jay B. Nilson and Donald L. Wartner entitled "Data Storage Apparatus Employing A Single Magnetic Disk," and U.S. Pat. No. 3,609,722 issued Sept. 28, 1971, in the name of George E. Zenzefilis, entitled "Center Sealing Data Disc Cassette and Processing Machine."